It was reported that sol-gel processed SiO2-coating effects of Ce3+: YAG phosphor on and thermal reliability enhancements in terms of quantum efficiency and optical characteristics. This study found improved light extraction efficiencies of glass phosphor, and increased quantum efficiency 3.95% of SGCeYDG in comparison to un-coated CeYDLTG. In the thermal reliability tests, Lumen degradation and chromaticity shift (ΔE) in the SGCeYDG thermally agd at 150, 250, 350, and 450°C, respectively, are also presented and compared with those of CeYDG. The results clearly demonstrated that the SGCeYDG exhibited better thermal stability on lumen degradation, and chromaticity shift than CeYDG’s. The navel high performance thermal-stable glass has been essentially critical to the application areas of LED modules where high-power leading high-operation-temperature and absolute thermal reliability are required for developing the nextgeneration solid-state lighting industry.
In this paper, we would like to report the following two subjects:(1) Thermal
decay mechanisms of phosphor-doped silicone in high power phosphor-converted
white light emitting diode (PC-WLED) module and (2) Thermal aging variations of
light profile and output power of blue LED modules having a polycarbonate lens and
silicone as an encapsulant.
Although silicone degradation attributed to the final thermal degradation, it is not
a dominant factor until a much thicker silicone is employed in PC-LEDs. The major
degradation mechanism of the PC-LEDs results from the higher doping concentration
of Ce:YAG in silicone. However, the negligible difference of fluorescent lifetimes
among the test samples before and after thermal aging (at 150°C for 500hrs)
eliminated any significant quenching processes that existed in our aged samples. The
emission spectra suggest that a higher doping concentration in silicone causes a higher
degree of loss at the emission wavelength of Ce:YAG, namely 570nm. Therefore,
minimizing any mismatch of the refractive index, thermal expansion , and chemistry
between the phosphor and the silicone is a new sign of improving thermal reliability
for high power PC-LEDs.
Thermal aging variations of light profile and output power of LED modules
fabricated by three manufacturers (namely, Type I, II, and III) were investigated
experimentally and numerically. Both experimental results and simulation results
suggested that improving the lens/ encapsulant materials and packaging designs are
essential to not only greatly extend the product lifetime but also enhance the light quality of LED modules as illumination sources.
Index Terms -High-powered phosphor-converted white-light-emitting diodes
(PC-WLEDs), lumen loss, chromaticity shift, silicone, polycarbonate, thermal aging,
etc.
The high-power phosphor-based white-light-emitting diodes (LEDs) after thermal aging at 150°C and 500 hours are
studied experimentally. The white-light LEDs formed by three combinations of different thicknesses and concentrations
of the silicone YAG phosphor are 1 mm and 5.48%, 2mm and 3.2%, 3mm and 2.4%, respectively. The results showed
that the lumen loss, chromaticity (CIE) shift, and spectrum intensity reduction in yellow YAG phosphor of the highpower
white-light LEDs increased as the silicone YAG phosphor concentration increased. These were due to that the
transmittance loss and the refractive index variation of the silicone YAG phosphor increased as the aging time increased
and resulted in lower emission efficiency of the high-power white-light LEDs. However, the lumen loss and CIE shift
did not significantly depend on the thickness of the silicone YAG phosphor. The likely cause for the transmittance
reduction and refractive index variation increased is that the thermal effect increased after thermal aging. As a result, the
key of high-power phosphor-based white-light LEDs module package related degradation mode under thermal aging
was identified as the decay of the silicone YAG phosphor, evidenced by secondary-ion mass spectroscopy (SIMS)
analyses. This study clearly indicates that in order to maintain luminous power and minimize color shift of the highpower
white-light LEDs modules, a lower concentration of the YAG phosphor for use in packaging of the phosphorbased
white-light LEDs modules is essential.
One of the greatest challenges in the packaging of laser modules using laser welding technique is to use a reliable and accurate joining process. However, during welding, due to the material property difference between welded components, the rapid solidification of the welded region and the associated material shrinkage often introduced a post-weld-shift (PWS) between welded components. For a typical single-mode fiber application, if the PWS induced fiber alignment shift by the laser welding joining process is even a few micrometers, up to 50 % or greater loss in the coupled power may occur. The fiber alignment shift of the PWS effect in the laser welding process has a significant impact on the laser module package yield. Therefore, a detailed understanding of the effects of PWS on the fiber alignment shifts in laser-welded laser module packages and then the compensation of the fiber alignment shifts due to PWS effects are the key research subjects in laser welding techniques for optoelectronic packaging applications. Previously, the power losses due to PWS in butterfly-type laser module packages have been qualitatively corrected by applying the laser hammering technique to the direction of the detected shift. Therefore, by applying an elastic deformation to the welded components and by observing the corresponding power variation, the direction and magnitude of the PWS may be predicted. Despite numerous studies on improving the fabrication yields of laser module packaging using the PWS correction in laser welding techniques by a qualitative estimate, limited information is available for the quantitative understanding of the PWS induced fiber alignment shift which can be useful in designing and fabricating high-yield and high-performance laser module packages. The purpose of this paper is to present a quantitative probing of the PWS induced fiber alignment shift in laser-welded butterfly-type laser module packaging by employing a novel technique of a high-magnification camera with image capture system (HMCICS). The benefit of using the HMCICS technique to determine the fiber alignment shift are quantitatively measure and compensate the PWS direction and magnitude during the laser-welded laser module packages. This study makes it possible to probe the nonlinear behavior of the PWS by using a novel HMCICS technique that
results in a real time quantitative compensation of the PWS in butterfly-type laser module packages, when compared to the currently available qualitatively estimated techniques to correct the PWS2. Therefore, the reliable butterfly-type laser modules with high yield and high performance used in lightwave transmission systems may thus be developed and fabricated.
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